Plastic lens and optical pickup device

ABSTRACT

A lens has a flange part at the outer periphery of its surface. A flange surface of the flange part is higher than the lens surface. The flange surface has a marking to identify a production jig, for example.

CROSS-REFERENCE TO RELATED APPLICATION

This is a Continuation of application Ser. No. 12/216,775 filed Jul. 10,2008 which is a Division of application Ser. No. 10/721,458 filed Nov.26, 2003, which claims priority from Japanese Patent Application SerialNo. 2002-342775. The disclosures of the prior applications are herebyincorporated by reference herein in their entirety.

BACKGROUND

The present invention relates to a plastic lens used in optical elementssuch as cameras and optical disc apparatus, a manufacturing method ofthe same, a production tracing management method for a plastic lens, andan optical pickup device having a plastic lens.

Digital cameras and optical disc apparatus have been spread. The opticaldisc apparatus, for example, have an optical pickup device for readinginformation stored on an optical storage medium. The optical pickupdevice has a pickup lens for focusing light from a light source on theoptical storage medium.

The pickup lens is generally manufactured by molding glass or plasticsuch as polyolefin resin or acrylic resin. A plastic pickup lens isproduced by injection molding, transfer molding, or other moldingtechniques using a mold. In an injection molding process, for example,resin is poured into a cavity in the mold through a gate and allows itto cool to solidify, thereby producing a pickup lens.

This kind of plastic lenses are mass-produced to reduce unit price.Thus, a plurality of lenses are simultaneously produced using a moldhaving a plurality of cavities. For example, eight lenses are producedat a time using a mold having eight cavities. Though the quality of thelens formed in each cavity is preferably the same, it may vary inpractice. Further, the quality may vary by mold and molding device.

A technique of marking a plastic lens is disclosed in JapaneseUnexamined Patent Application Publication No. 2002-122711, and U.S.patent application Publication Ser. No. 2001/0017733, Asakura, forexample. To distinguish a lens surface, this technique deposits acoating film that serves as a marking on the peripheral area of one lenssurface by printing, coating, or evaporation. Thus, the material of thelens and the marking are different; therefore, this technique furtherrequires a marking process in addition to a lens molding process whenproducing a lens by injection molding.

Another marking technique for another object is disclosed in JapaneseUnexamined Patent Application Publication No. 2000-111709. Thistechnique creates a convexity or concavity on a flange surface of anoptical component to indicate a resin injection position. No mention ismade to a manufacturing method nor mold used in this technique. Sincethe convexity or concavity is placed on the upper surface of the flangepart, however, the marking is likely to chip away or get contaminatedwhen put on a desk or by handling. This causes to fail to convey markinginformation properly. Besides, the whole purpose of the markingdescribed in this technique is to align the position of a gate, not toidentify a lens nor track the production of the lens during theproduction process. This is obvious from the fact that the marking isformed only in one place, thus unable to distinguish between a pluralityof lenses. In addition, the convex marking in the structure shown inFIG. 5 of the publication projects above the upper flange surface by 0.1to 0.5 mm. Thus, the lens is unstable when placed with the surfacehaving the convex marking facing down. Further, the convex marking canchip away by contact with another component. The concavity formed at theupper flange surface, on the other side, is likely to suffer fromaccumulation of contamination, for example glue, which reducesvisibility. It is therefore preferred that the marking is visible evenif it is formed at the other portion than the flange surface, and itdoes not touch another component. These references are incorporatedherein.

As described earlier, the quality of lenses produced by molding may varyby mold or cavity. This raises the need for quality control, productionmanagement, and production tracing of a lens after mounted on an opticaldevice. It is thus preferred to create a marking on a lens itself toidentify a production jig such as a mold and a cavity or a productionline process. The creation of the marking, however, should notdeteriorate the performance of the lens. The lens is an opticalcomponent, and certain performance is required accordingly. Creating themarking on an optical functional part at the center of the lens, forexample, should be avoided since this has an adverse effect on theoptical function.

Further, if a marking is broken by abrasion with another component, itnot only reduces visibility of the marking, but also deteriorates theoptical performance of the optical functional part due to a broken dustattached thereto.

SUMMARY

An object of the present invention is to provide a plastic lens having amarking optimally created thereon, an optical pickup device, and amanufacturing and production management method of the lens suitable forintegrally molding such a marking by injection molding.

To these ends, according to the present invention, there is provided aplastic lens produced by injection molding of resin material, includinga flange part on a periphery of a lens surface, a flange surface on atleast one side of the flange part having a part higher than the lenssurface and a depressed part formed on at least a part thereof; and amarking integrally molded by injection molding to a marking surface ofthe depressed part, a highest point of the marking being lower than ahighest point of the flange surface.

Preferably, the flange part has a cutout portion in an outer sidesurface thereof. Further, the flange surface is preferablymirror-finished at least in a vicinity of an area where the marking isformed.

According to the present invention, there is provided a plastic lensproduced by injection molding of resin material, including a flange parton a periphery of a lens surface, a flange surface on at least one sideof the flange part having a part higher than the lens surface; and amarking integrally molded to the flange surface by injection molding,for identifying a production jig used to produce the lens.

Preferably, a highest point of the marking is lower than a highest pointof the flange surface. The marking is preferably formed in a depressedpart of the flange surface. Further, it is preferred that the flangepart has a cutout portion in an outer side surface thereof. The flangesurface is preferably mirror-finished at least in a vicinity of an areawhere the marking is formed.

According to the present invention, there is provided an optical pickupdevice having the above described lens.

According to the present invention, there is provided a method ofmanufacturing a plastic lens produced by injection molding of resinmaterial in a mold cavity, the lens having a marking on a different partfrom an optical functional part. The method includes the steps ofproviding a mold part for one side comprising a first mold member and asecond mold member, the first mold member and the second mold memberforming a part of the mold cavity; providing a mold part for other sideto form the mold cavity cooperable with the mold part for one side whenassembled; injecting resin material into the mold cavity; forming theoptical functional part of one side of the lens, with the first moldmember; and forming the different part of one side of the lens than theoptical functional part and the marking thereon, with the second moldmember.

Preferably, the different part of one side of the lens than the opticalfunctional part has a flange part on a periphery of a lens surface. Aboundary between the first mold member and the second mold member ispreferably located near an innermost periphery of the flange part of thelens. The flange part of the lens preferably has a depressed part on atleast a part thereof and a marking integrally molded to the depressedpart by injection molding. Further, it is preferred that the flange partof the lens includes a flange surface on at least one side of the flangepart having a part higher than the lens surface and a depressed part onat least a part thereof, and a marking integrally molded by injectionmolding to a marking surface of the depressed part, a highest point ofthe marking being lower than a highest point of the flange surface.Furthermore, the flange surface preferably has a cutout portion in anouter side surface thereof. The flange surface of the flange part isdesirably mirror-finished at least in a vicinity of an area where themarking is formed.

According to the present invention, there is provided a method oftracing production of a plastic lens produced by injection molding ofresin material. The method includes the step of manufacturing theplastic lens comprising a flange part on a periphery of a lens surface,a flange surface on at least one side of the flange part having a parthigher than the lens surface, and a marking integrally molded to theflange surface by injection molding; and the step of tracing productionof the lens by use of the marking formed on the lens.

According to the present invention, there is provided another method oftracing production of a plastic lens produced by injection molding ofresin material. The method includes the step of manufacturing theplastic lens comprising a flange part on a periphery of a lens surface,a flange surface on at least one side of the flange part having a parthigher than the lens surface, and a marking integrally molded to theflange surface by injection molding, a highest point of the markingbeing lower than a highest point of the flange surface; and the step oftracing production of the lens by use of the marking formed on the lens.

Preferably, each position of the marking formed on each lens iscircumferentially different on the flange surface to distinguishproduction of one lens from another. Further, it is preferred that eachshape of the marking formed on each lens is different to distinguishproduction of one lens from another.

According to the present invention, there is provided a mold formanufacturing a plastic lens produced by injection molding of resinmaterial and having a marking on a part different from an opticalfunctional part. A mold at a side where a marking will be formedincludes a first mold member to form an optical functional part of oneside of the lens, and a second mold member to form a part different fromthe optical functional part of one side of the lens. The second moldmember is separatable from the first mold member and has a portion toform the marking.

The present invention can provide a lens where a marking for productiontracing is created in the most effective way, a manufacturing methodthereof, and an optical pickup device.

The above and other objects, features and advantages of the presentinvention will become more fully understood from the detaileddescription given hereinbelow and the accompanying drawings which aregiven by way of illustration only, and thus are not to be considered aslimiting the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are a top plan view and a side plan view, respectively,of a lens according to the present invention.

FIG. 2 is an enlarged sectional view of a flange part of a lensaccording to the present invention.

FIG. 3 is an enlarged sectional view of a flange part of a lensaccording to the present invention.

FIG. 4 is an enlarged sectional view of a flange part of a lensaccording to the present invention.

FIG. 5 is an enlarged sectional view of a flange part of a lensaccording to the present invention.

FIGS. 6A and 6B are a top plan view and a side plan view, respectively,of a lens according to the present invention.

FIG. 7 is a sectional view showing production of a lens according to thepresent invention.

FIGS. 8A and 8B are sectional views showing production of a lensaccording to the present invention.

FIG. 9 is a view showing an optical pickup device according to thepresent invention.

DETAILED DESCRIPTION OF EMBODIMENTS Embodiment 1

A lens according to the first embodiment of the present invention willbe explained hereinafter, taking a pickup lens as an example, withreference to FIGS. 1A, 1B, and 2.

FIG. 1A is a top plan view of a lens 1. FIG. 1B is a side plan view ofthe lens 1, and the left half shows a cross-section of the lens. Asshown therein, a flange part 2 is formed on the outer periphery of thelens 1. The flange part 2 has an upper flange surface 21, which facestoward an optical recording medium when the lens 1 is mounted on anoptical disc apparatus to read information from the optical recordingmedium. The other side is a lower flange surface 23. The flange part 2,which is strip-shaped, is placed on the entire periphery of an opticalfunctional part of the lens 1. The flange part 2 is not necessarilycompletely around the periphery, and it may have a notch at a part ofthe periphery.

As shown in FIG. 1B, the highest part of the upper flange surface 21 ishigher than the upper surface of the optical functional part in theoptical axis direction. Thus, when the lens 1 is placed on a desk or soon with the upper flange surface 21 facing down, the upper flangesurface 21, not the optical functional part, touches the desk. Thisprevents the optical functional part from being damaged by contact witha desk and the like. This also prevents it from being damaged by directcontact with an optical recording medium after the lens 1 is mounted toan optical disc apparatus.

The lens 1 in this example has a diameter of 5.8 mm, including theflange part 2. The flange part 2 has a vertical width of 0.9 mm. A lensin another example has a diameter of 3.8 mm.

As shown in FIG. 1A, the upper flange surface has a depressed part 20.Markings 3 a and 3 b are created in two different positions on thedepressed part 20. The markings are used to identify a production jigsuch as a mold, a cavity, or an injection molder. The markings 3 a and 3b are formed not to be higher than the highest part of the upper flangesurface 21. The markings 3 a and 3 b are integrally molded to the upperflange surface 21 by providing a mold for the surface with the shapescorresponding to the markings. The markings are placed in two differentpositions to distinguish lenses produced with different production jigsby changing their relative positions. A cavity, for example, isdistinguishable by changing the relative positions of the markingsaccording to a cavity. Specifically, for the first cavity, the markingsare placed in such positions that the angle between the lines connectingthe center of the lens to each of the markings is 180 degrees. For thesecond cavity, on the other hand, the markings are placed incircumferentially different positions in which the above angle is 120degrees.

The markings 3 a and 3 b each have a shape of half-round convex. Thougha concave shape can also serve as a marking, the convex shape ispreferable because of ease of mold production. The markings 3 a and 3 bin this example have a height of 0.02 to 0.03 mm. The half-round convexshaped markings is advantageous in that mold production is easy. Theshape of the marking 3 is not necessarily half-round, and it may beanother shape such as a square or a cross, or it may be a shape of aletter such as an alphabet or a number. Though the markings 3 a and 3 bhave the same shape in this example, they may have a different shape.The number of the markings 3 may be more than two. Or, it may be one ifthe shape varies by unit to identify such as by cavity. Further, if thelens has a marking indicating the position of a gate, checking therelative position of this marking and the marking 3 allowsidentification. Furthermore, one lens may have markings for identifyingboth a mold and a cavity. For example, the marking for identifying amold may be two parallel convexities, while the marking for identifyinga cavity may be one convexity, thereby distinguishing between the two.

FIG. 2 is an enlarged sectional view of the flange part 2 of the lens 1.If the marking 3 is placed on the highest part of the upper flangesurface 21 in the optical axis direction, the fine marking 3 may bebroken to be invisible by abrasion with the surface where the lens isplaced during the production process or by contact with an opticalrecording medium when the lens 1 is mounted to an optical pickup device.Further, if the marking 3 is chipped away, it may generate plasticparticles or dust, which causes a problem. A solution to the aboveproblems is to create a depressed part 20 on at least a part of theflange surface, and form the marking 3 thereon to be lower than thehighest part of the upper flange surface 21. In this embodiment, theflange surface has a depressed part 20 formed in the circumferentialdirection, and the marking 3 is placed on the depressed part 20 so thatit is lower than the highest part of the upper flange surface 21. Havingthe marking 3 not protruding above the upper flange surface 21, thisembodiment can reduce the risk of damage by abrasion.

In the upper flange surface 21, the surface of the depressed part 20where the marking 3 b is formed is a marking surface 211. The markingsurface 211 is lower than the flange surface 21 in the optical axisdirection. For easier release of a molded product from a mold, themarking surface 211 is lower than the highest point of the upper flangesurface 21 preferably by less than 100 μm, and more preferably by 50 μmand less. The marking surface 211 may be higher or lower than the lenssurface.

The upper flange surface 21 including the marking surface 211 ismirror-finished in a polishing process of a mold member. Since a surfacewith a mirror finish has higher reflectivity than a surface without amirror finish, the bright and dark contrast is great between the marking3 and the other part. There is thus an advantage of the increasedvisibility of the marking 3. The mirror finish may be applied to thewhole area of the upper flange surface 21 or to a limited area in thevicinity of the marking. When creating a marking on the marking surface211, the ratio M/W of the width (M) of the bottom of the marking and thewidth (W) of the marking surface is preferably 2 to 10, and morepreferably 2.5 to 5.

Preferably, the marking surface 211 does not extend to the outerperipheral part of the lens by forming the highest portion in the flangesurface at the outer peripheral part of the marking surface 211. Thisprevents an adhesive from flowing thereinto to make the markinginvisible.

Another solution to the problem of damage by abrasion is to place themarking 3 not on the upper flange surface 21 but on the other partoutside of the optical functional part, for example, the outermostperipheral area of the lens surface. However, this has the problem thatthe marking 3 is blocked from view by the flange part 2. In addition, tohave a large effective diameter or optical functional part, it is notpreferred to place the marking 3 on the lens surface. The presentembodiment thus places the marking 3 on the flange part 2. Since themarking 3 is placed on the upper flange surface 21 in this embodiment,the marking 3 is still visible after the lens 1 is attached to anoptical disk apparatus.

In this embodiment, the lowest point of the upper lens surface and thehighest point of the lower lens surface are not in correspondingpositions as shown in FIG. 2. A boundary Q between the lower flangesurface 23 and the lens surface is located at the outer side of aboundary P between the upper flange surface 21 and the lens surface.This ensures the marking surface to still have a sufficient width whenthe thickness of the lens is reduced and that of the flange part isreduced accordingly.

Embodiment 2

A lens according to the second embodiment of this invention is differentfrom the lens according to the first embodiment in the shape of theflange part. Other aspects are the same as the first embodiment, andtherefore same explanation will be shortened.

FIG. 3 is an enlarged sectional view of the flange part of the lens inthe second embodiment of the invention. As shown therein, the flangesurface has a depressed part, and the bottom surface of the depressedpart is a marking surface 211. The marking surface 211 is lower than theupper flange surface 21. The marking surface 211 extends to the innerperiphery of the flange part. It is also possible that the upper flangesurface 21 lies on both the outer periphery and the inner periphery ofthe flange part with the marking surface 211 lying therebetween, asshown in FIG. 3. The height of the upper flange surface 21 at the outerand inner periphery is not necessarily equal.

The upper flange surface 21 is preferably perpendicular to the opticalaxis direction; however, the surface may be inclined.

In the following, a process of manufacturing the lens having the aboveconfiguration by injection molding will be briefly explained.

The process begins with creation of a mold. The mold has a shapecorresponding to the shape of an article to be produced. The mold usedin this embodiment has such a shape as to form a marking on the upperflange surface 21.

The next is setup of the mold in an injection molder. Then, in theinjection molder, resin is injected into a cavity in the mold through agate. The resin in the cavity then cools to solidify. A lens is therebyproduced.

As described above, the lens according to this embodiment has themarking created in the most effective manner to identify a productionjig such as a cavity and a mold. This provides the same advantage as thelens according to first embodiment.

Embodiment 3

A lens according to the third embodiment of this invention is differentfrom the lens according to the first embodiment in the position of themarking. Other aspects are the same as the first embodiment, andtherefore same explanation will be shorten.

FIG. 4 is an enlarged sectional view of the flange part of the lensaccording to the third embodiment. As shown therein, the marking 3 b,which is a half-round convex shape, is created on the upper flangesurface 21. The marking 3 b is formed to be lower than the highest partof the upper flange surface 21. In the lens according to thisembodiment, the depressed part 20 is formed at the outer part of theupper flange surface 21.

As described above, the lens according to the third embodiment of thisinvention has the marking created in the most effective manner toidentify a production jig such as a cavity and a mold. It provides thesame advantage as the lens according to above embodiments.

Embodiment 4

A lens according to the fourth embodiment of this invention is differentfrom the lens according to the first embodiment in the shape of theouter side surface of the flange part. Other aspects are the same as thefirst embodiment, and therefore same explanation will be shortened.

FIG. 5 is an enlarged sectional view of the flange part of the lens inthe fourth embodiment. The lens is attached to a pickup holder 4 of anoptical pickup device. As shown therein, the flange part 2 of the lenshas a cutout portion 221 at its outer side surface. The cutout portion221 has such a shape that the upper part of the outer side surface ofthe flange part 2 is cut away. Though the cutout portion 221 is providedon the entire periphery of the flange part 2 in this example, it is notnecessarily on the entire periphery.

A pickup holder 4 holds the lens by the lower flange surface 23 and aside flange surface 22. Specifically, the pickup holder 4 has a mountingportion 41 where the lower flange surface 23 is placed and a protrudingportion 42 projecting upward at the outer side of the mounting portion41.

The bottom surface of the cutout portion 221 is at substantially thesame height as the top surface of the protruding portion 42 of thepickup holder 4. In other words, the height H of the protruding portion42 is substantially the same as the distance between the bottom surfaceof the cutout portion 221 and the lower flange surface 23.

The lens 1 is attached to the pickup holder 4 generally with anadhesive. The cutout portion 221 serves as an adhesive reservoir. Thisprevents that an adhesive flows into the area of the marking 3 b to makethe marking 3 b invisible.

Embodiment 5

A lens according to the fifth embodiment of this invention is differentfrom the lens according to the first embodiment in the position andshape of the marking. Other aspects are the same as the firstembodiment, and hence same explanation will be shortened.

FIGS. 6A and 6B are a top plan view and a side plan view, respectively,of a lens in the fifth embodiment. As shown in FIG. 6A, the marking 3 b,which is formed on the upper flange surface 21, has a convex semicylindrical shape protruding toward the center of the lens. The uppersurface of the marking 3 b is at the same level as the upper flangesurface 21 as shown in FIG. 6B.

As described above, the lens according to the fifth embodiment of thisinvention has the marking created in the most effective manner toidentify a production jig such as a cavity and a mold. It therebyprovides the same advantage as the lens according to the aboveembodiments.

The convex shape protruding toward the center of the lens is notnecessarily semi cylindrical, and it may be triangular, quadrilateral,and so on.

Embodiment 6

A lens according to the sixth embodiment of this invention has the sameshape as the lens according to the first embodiment. This embodimentuses inserts as some of the mold members to produce the lens. Otheraspects are the same as the first embodiment, and therefore sameexplanation will be shortened.

FIG. 7 is a side plan view of a lens according to the sixth embodimentof this invention. Inserts 51 and 52 are also shown therein. The inserts51 and 52 are mold members to shape a portion including an opticalfunctional part of the lens 1. Members 53 and 54 are mold members toshape the flange part 2. The mold members 53 and 54 are made separatelyfrom the inserts 51 and 52. On each side, mold members 51 and 53, or 52and 54 form each side of mold part. When assembled, those mold membersform a mold cavity, in which resin material is injected and molded. Forthe lens surface without marking, use of the insert may be eliminated.Specifically, the insert 52 may not be separated from but integrated tothe mold member 54.

As known from the description, the optical functional part means theaperture of the luminous flux that actually passes through the lens,which differs according to use. For example, NA=0.45 for CD, NA=0.60 forDVD, and NA=0.85 for Blu-ray disc. The optical functional part is placedin the inner part of the lens surface.

A parting line that separates the inserts 51 and 52 from other moldmembers is somewhere between the outermost periphery of the opticalfunctional part of the lens and the innermost periphery of the markingsurface. Preferably, the parting line is at the inner peripheral area ofthe flange part 2. This is for the reasons including the following. Thefirst is that, even if flash, which is a sharp protrusion, is formed asresin solidifies at the boundary between the inserts 51 or 52 and othermold members, it causes no problem provided it is less than the depth ofthe depressed part. The second reason is that, if the parting line is atthe boundary between the upper flange surface 21 and the lens surface,it is difficult to apply a mirror finish to the upper flange surface 21.

The mold member 53 has a portion to define the shape of a marking at thepart facing the upper flange surface 21 of the flange part. This portionallows forming the marking 3 b on the flange surface by injectionmolding.

As described above, the insert 51 is placed in the mold to shape theoptical functional part mainly. This is to facilitate the adjustment inthe production of the lens 1. When producing the lens 1, a marking isintegrally molded on the upper flange surface. It is thus preferred thatthe mold members for the optical functional part can rotate along theoptical axis without changing the position of the mold members for theflange part, which has the cavity number or other marking. The use ofthe inserts 51 eliminates the need to create another united molding partfor a marking on the flange part additionally.

For example, if the lens produced with the insert placed at a certainposition turns out to be poor in quality, the lens can be reproducedafter rotating the insert. The position of the insert is repeatedlyadjusted until the lens quality improves.

In this embodiment, each of the mold members 53 and 54 may be composedof two or more pieces.

The present invention places a marking not on the optical functionalpart but on the other part of the lens. This is especially suitable forthe manufacturing method that uses the inserts 51 and 52 as the moldparts to shape the optical functional part. Since the insert 51 is aseparate part from the mold member 53, it reduces the risk of damagingthe insert 51 during the process of forming a shape corresponding to adesired marking on the mold member 53.

Embodiment 7

A lens according to the seventh embodiment of this invention isdifferent from the lens according to the first embodiment in the shapeof the marking. Other aspects are the same as the first embodiment, andhence an explanation will be omitted.

FIG. 8A is an enlarged sectional view of the flange part of the lensaccording to the fourth embodiment of the invention. FIG. 8B is asectional view showing the above lens placed in the mold parts includingthe inserts 51 and 52. As shown therein, the marking 3 b is a half-roundconcave shape formed on the upper flange surface 21. Since the marking 3b is depressed below the upper flange surface 21, it does not touch thesurface where the lens is placed during the production process. Further,it does not touch an optical recording medium when the lens 1 is mountedto an optical pickup device. This reduces the risk of damage by abrasionwith the surface or the optical recording medium.

As shown in the figure, the mold members to shape the optical functionalpart of the lens 1 are the inserts 51 and 52. The mold members to shapethe flange part 2, on the other hand, are the mold members 53 and 54,which are made separately from the inserts 51 and 52.

Embodiment 8

The eighth embodiment of this invention relates to an optical pickupdevice having the lens according to one of the first to seventhembodiments.

FIG. 9 shows the structure of an optical pickup device 100 where thelens 1 is mounted. The lens 1 is fixed at four points with the pickupholder 4. Specifically, the flange part 2 of the lens 1 is attached tothe pickup holder 4 with an adhesive.

The marking on the flange part 2 is visible to the eye with or without ahand lens when the lens 1 is mounted on the optical pickup device 100.For a lens with a certain defect, its production process can be trackedusing the marking to identify a production jig, mold, production lineprocess, production place, producer, and so on.

Another Embodiment

The lens according to the present invention may be a meniscus lens withone side convex and the other concave, for example.

From the invention thus described, it will be obvious that theembodiments of the invention may be varied in many ways. Such variationsare not to be regarded as a departure from the spirit and scope of theinvention, and all such modifications as would be obvious to one skilledin the art are intended for inclusion within the scope of the followingclaims.

1. A plastic lens for an optical pick-up device and for a blu-rayrecording medium, the plastic lens being formed by an injection moldingof a resin material, the plastic lens comprising: a first lens surfacethat is arranged at an optical recording medium side; a second lenssurface that is opposed to the first lens surface; a flange part that isprovided at peripheries of the first and second lens surfaces andcomprises flange surfaces that are opposed to each other, the flangesurface at the optical recording medium side comprising a projectingsurface and a marking surface, the projecting surface projecting to theoptical recording medium side when viewed from the first lens surfaceand the marking surface, the marking surface being configured to be aring shape and positioned closer to the first lens surface than theprojecting surface; and a first marking that is integrally formed on themarking surface by the injection molding and comprises a projectingshape that projects from the marking surface to the optical recordingmedium side, a level of a top end of the first marking being configurednot to overreach a level of the projecting surface, wherein a peripheryof the first marking is substantially surrounded by the marking surface,and an area of the marking surface surrounding the first marking ismirror-finished.
 2. The plastic lens for the optical pick-up deviceaccording to claim 1, wherein the first marking comprises an islandshape when viewed from above.
 3. The plastic lens for the opticalpick-up device according to claim 1, wherein the first marking comprisesa rounded shape when viewed from above.
 4. The plastic lens for theoptical pick-up device according to claim 1, wherein a shape of thefirst marking when viewed along a direction crossing an optical axisorthogonally is rounded.
 5. The plastic lens for the optical pick-updevice according to claim 1, wherein a side surface of the flange partis attached to a pick-up holder via an adhesive.
 6. The plastic lens forthe optical pick-up device according to claim 5, wherein the flange partcomprises a cutout portion that receives the adhesive.
 7. The plasticlens for the optical pick-up device according to claim 1, wherein thefirst marking is for identifying at least one of a mold, a cavity, andan injection molder which have been used for producing the plastic lens.8. The plastic lens for the optical pick-up device according to claim 1,wherein a level difference between the projecting surface and themarking surface is equal to or below 100 μm in an optical axisdirection.
 9. The plastic lens for the optical pick-up device accordingto claim 1, wherein, when a width of the first marking in a directioncrossing an optical axis orthogonally is M and a width of the markingsurface in the direction crossing the optical axis orthogonally is W,2<W/M<10 is satisfied.
 10. The plastic lens for the optical pick-updevice according to claim 1, further comprising: a second marking thatis integrally formed on the marking surface by the injection molding andcomprises a projecting shape that projects from the marking surface tothe optical recording medium side, a level of a top end of the secondmarking being configured not to overreach the level of the projectingsurface.
 11. The plastic lens for the optical pick-up device accordingto claim 10, wherein the second marking indicates information that isdifferent from information indicated by the first marking.
 12. Theplastic lens for the optical pick-up device according to claim 11,wherein the first marking is configured to be different from the secondmarking when viewing along a direction.
 13. The plastic lens for theoptical pick-up device according to claim 10, wherein at least one ofthe first and second markings is configured to be a single projectingportion.
 14. The plastic lens for the optical pick-up device accordingto claim 10, wherein the second marking is suitable for identifying aproduction jig.
 15. The plastic lens for the optical pick-up deviceaccording to claim 14, wherein a relative position between the first andsecond markings indicates a production jig that has been used forproducing the plastic lens.
 16. The plastic lens for the optical pick-updevice according to claim 15, wherein the relative position between thefirst and second markings indicates at least one of a mold, a cavity,and an injection molder.
 17. The plastic lens for the optical pick-updevice according to claim 10, wherein at least one of the first andsecond markings indicates a position of a gate.
 18. The plastic lens forthe optical pick-up device according to claim 10, wherein a relativeposition between the first and second markings indicates predeterminedinformation.
 19. The plastic lens for the optical pick-up deviceaccording to claim 18, wherein the relative position between the firstand second markings indicates a production jig that have been used forproducing the plastic lens.
 20. The plastic lens for the optical pick-updevice according to claim 19, wherein the relative position between thefirst and second markings indicates at least one of a mold, a cavity,and an injection molder.
 21. An optical pick-up device comprising theplastic lens of claim
 1. 22. A plastic lens for an optical pick-updevice and for a blu-ray recording medium, the plastic lens being formedby an injection molding of a resin material, the plastic lenscomprising: a first lens surface that is arranged at an opticalrecording medium side; a second lens surface that is opposed to thefirst lens surface; a flange part that is provided at peripheries of thefirst and second lens surfaces and comprises flange surfaces that areopposed to each other, the flange surface at an optical recording mediumside comprising a projecting surface and a marking surface, theprojecting surface projecting to the optical recording medium side whenviewed from the first lens surface and the marking surface, the markingsurface being configured to be a ring shape and positioned closer to thefirst lens surface than the projecting surface; a first marking that isintegrally formed on the marking surface by the injection molding andcomprises a projecting shape that projects from the marking surface tothe optical recording medium side, a level of the top end of the firstmarking being configured not to overreach a level of the projectingsurface; and a second marking that is integrally formed on the markingsurface by the injection molding and comprises a projecting shape thatprojects from the marking surface to the optical recording medium side,a level of a top end of the second marking being configured not tooverreach the level of the projecting surface, wherein a periphery ofthe first marking and periphery of the second marking are substantiallysurrounded by the marking surface respectively, and an area of themarking surface surrounding the first marking and an area of the markingsurface surrounding the second marking are mirror-finished respectively,and wherein the first marking indicates a position of a gate, and thesecond marking indicates predetermined information by itself or togetherwith the first marking.
 23. The plastic lens for the optical pick-updevice according to claim 22, wherein the predetermined information isfor identifying a production jig that has been used for producing theplastic lens.
 24. The plastic lens for the optical pick-up deviceaccording to claim 23, wherein the predetermined information is foridentifying at least one of a mold, a cavity, and an injection molderwhich have been used for producing the plastic lens.